1. Field of the Invention
The present invention relates to a video transmission apparatus which is capable of transmitting video signals, even from an isolated island or a remote place where no communication network is provided, through use of communication satellite lines.
2. Description of the Prior Art
With analog inmarsat A network, full duplex lines have been established with a transmission rate of 4800 bps between mobile earth station and land earth station for both forward channel and backward channel, thereby achieving telephone function. In addition, HSD (High Speed Data) service with an increased transmission rate of 64 Kbps for the forward channel has also been available. Video transmitting apparatus using such a service has been employed for the purposes of collecting news at an isolated island or a remote place through use of communications satellite. With the conventional apparatus, it has been the practice that when it is attempted to transmit video material via the 64 Kbps forward channel of the A network, the transmitting station makes a previous arrangement with the receiving station by using the telephone function, confirms that the receiving station is ready for reception; then switches the apparatus to the HSD service mode; and transmits video data either in real-time mode or storage mode, in a one-way fashion.
In the real-time mode, detection of transmission error at the receiving station is effected by performing real-time correction process at the receiving station without using the backward channel; thus, the telephone function can be retained for the backward channel.
In the storage mode, on the other hand, the telephone function is not available since the backward channel is occupied for the receiving station to detect transmission error in video transmission for each data block and send the result of the detection to the transmitting station. Furthermore, the switching of the apparatus to the telephone mode cannot be effected at the receiving station, and thus inconveniently no means for transmitting information is available at the receiving station.